## Feature request: generic biometric (face) unlock hook in the lock screen, similar to the existing fingerprint support

Right now `Service.qml` (`/usr/share/omarchy/shell/plugins/lock/Service.qml`) wires a dedicated `fingerprintPam` `PamContext` (`config: "omarchy-lock-fingerprint"`) that starts automatically as soon as the session lock goes `secure`, gated on a shell check that an `fprintd`-enrolled fingerprint exists (`fprintd-list "$USER" | grep -qi finger`).

There's no equivalent passive hook for face/camera-based auth. The only other PAM path, `omarchy-lock-password`, is only invoked once the user has typed a non-empty string into the password field and submitted it (`submitPassword()` requires `password.length === 0` to be false before calling `passwordPam.start()`), so it can't be used to drive an automatic, look-at-the-camera-and-unlock flow — a PAM module placed there only fires after a keystroke, defeating passive biometric unlock.

### Motivation

Several actively-maintained Linux face-auth stacks now exist (e.g. `chowdy` — https://github.com/q-artem/chowdy, IR-camera-only, PAM `sufficient` by design) that behave essentially like Windows Hello: look at the camera, get unlocked, no typing required, and they fail safe to password since the PAM rule is always `sufficient`. On hardware with an IR camera (fairly common on modern webcams, including many that also expose a plain RGB path under a different `/dev/videoN` node), this is a genuinely useful, secure local-only convenience — no cloud involved, same trust model as the existing fingerprint support.

### Request

A second, generic `PamContext` (e.g. `omarchy-lock-face`, or a rename of the fingerprint one to something like `omarchy-lock-biometric` if you'd rather not maintain two) that:
- starts automatically on `secure` (same trigger as `startFingerprint()` today), independent of whether a fingerprint is enrolled
- is gated on the presence of `/etc/pam.d/omarchy-lock-face` (or similar) existing, the same pattern used for `omarchy-lock-fingerprint`, so it's opt-in and does nothing on hardware/setups that haven't configured it
- retries/aborts the same way the fingerprint path does today (`fingerprintRetryTimer`, `abort()` on failure)

Happy to test against a PR if useful — currently running Omarchy on a laptop with a UVC webcam exposing both RGB and IR sensors, `chowdy` enrolled and working for `sudo`, just can't hook it into the lock screen without this.